The present invention relates generally to control systems. More specifically, the present invention relates to a drive system for controlling the longitudinal movement and rotational position of an elongate member.
Each year roughly 200,000 patients are diagnosed with brain tumors in the United States. Roughly 17,000 of these tumors are “benign,” meaning that the tumor mass is not cancerous. However, the other roughly 183,000 of these tumors are “malignant” (i.e., cancerous), meaning that they are capable of causing or contributing to patient death. Approximately 10% of cancerous brain tumors are “primary” tumors, meaning that the tumors originate in the brain. The primary tumors typically consist of brain tissue with mutated DNA that aggressively grows and displaces or replaces normal brain tissue. The most common of the primary tumors are known as gliomas, which indicate cancer of the glial cells of the brain. In most instances, primary tumors appear as single masses. However, these single masses can often be quite large, irregularly-shaped, multi-lobed and/or infiltrated into surrounding brain tissue.
Primary tumors are generally not diagnosed until the patient experiences symptoms, such as headaches, altered behavior, sensory impairment, or the like. However, by the time the symptoms develop the tumor may already be large and aggressive.
One well known treatment for cancerous brain tumors is surgery. In particular, surgery involves a craniotomy (i.e., removal of a portion of the skull), dissection, and total or partial tumor resection. The objectives of surgery include removal or lessening of the number of active malignant cells within the brain, and a reduction in the pain or functional impairment due to the effect of the tumor on adjacent brain structures. However, by its very nature, surgery is highly invasive and risky. Furthermore, for some tumors surgery is often only partially effective. In other tumors, the surgery itself may not be feasible, it may risk impairment to the patient, it may not be tolerable by the patient, and/or it may involve significant cost and recovery.
Another well known treatment for cancerous brain tumors is stereotactic radiosurgery (SRS). In particular, SRS is a treatment method by which multiple intersecting beams of radiation are directed at the tumor such that the point of intersection of the beams receives a lethal dose of radiation, while tissue in the path of any single beam remains unharmed. SRS is non-invasive and is typically performed as a single outpatient procedure. However, confirmation that the tumor has been killed or neutralized is often not possible for several months post-treatment. Furthermore, in situations where high doses of radiation may be required to kill a tumor, such as in the case of multiple or recurring tumors, it is common for the patient to reach the “toxic threshold” prior to killing all of the tumors, where further radiation is inadvisable.
More recently, the treatment of tumors by “heat” (also referred to as hyperthermia or thermal therapy) has been developed. In particular, it is known that above 57° C. all living tissue is almost immediately and irreparably damaged and killed through a process called coagulation necrosis or ablation. Malignant tumors, because of their high vascularization and altered DNA, are more susceptible to heat-induced damage than normal tissue. Various types of energy sources may be used, such as laser, microwave, radiofrequency, electric, and ultrasound sources. Depending upon the application and the technology, the heat source may be extracorporeal (i.e., outside the body), extrastitial (i.e., outside the tumor), or interstitial (i.e., inside the tumor).
Interstitial thermal therapy (ITT) is a process designed to heat and destroy a tumor from within the tumor. One advantage of this type of therapy is that the energy is applied directly to the tumor rather than passing through surrounding normal tissue. Another advantage of the type of therapy is that the energy deposition is more likely to be extended throughout the entire tumor.
One exemplary ITT process begins by inserting an optical fiber into the tumor, wherein the tumor has an element at its “inserted” end that redirects laser light from an exterior source in a direction generally at right angles to the length of the fiber. The energy from the laser thus extends into the tissue surrounding the end or tip and effects heating. The energy is directed in a beam confined to a relatively shallow angle so that, as the fiber is rotated, the beam also rotates around the axis of the fiber to effect heating of different parts of the tumor at positions around the fiber. The fiber can thus be moved longitudinally and rotated to effect heating of the tumor over the full volume of the tumor with the intention of heating the tumor to the required temperature without significantly affecting the surrounding tissue.
The fiber used in the ITT process may be controlled and manipulated by a surgeon with little or no guidance apart from the surgeon's knowledge of the anatomy of the patient and the location of the tumor. Therefore, it is difficult for the surgeon to effect a controlled heating which heats the entire tumor to a required level while also minimizing damage to the surrounding tissue.
It is known that the location of tumors and other lesions to be excised can be determined using a magnetic resonance imaging system. Although these imaging systems have been helpful to assist the surgeon in determining a location of the tumor to be excised, use of the imaging systems ended once the location of the tumor was mapped out for the surgeon. In particular, previous excision procedures required the removal of the patient from the imaging system prior to commencing treatment. However, movement of the patient, together with the partial excision or coagulation of some of the tissue, can significantly change the location of the tumor to be excised. As a result, any possibility of providing controlled accuracy in the excision is eliminated.
It is also known that magnetic resonance imaging systems can be used by modification of the imaging sequences to determine the temperature of tissue within the image and to determine changes in that temperature over time.
U.S. Pat. No. 4,914,608 (LeBiahan) assigned to U.S. Department of Health and Human Services issued Apr. 3, 1990, discloses a method for determining temperature in tissue.
U.S. Pat. No. 5,284,144 (Delannoy) also assigned to U.S. Department of Health and Human Services and issued Feb. 8, 1994, discloses an apparatus for hyperthermia treatment of cancer in which an external, non-invasive heating system is mounted within the coil of a magnetic resonance imaging system. The disclosure is speculative and relates to initial experimentation concerning the viability of MRI measurement of temperature in conjunction with an external heating system. The disclosure of the patent has not led to a commercially viable hyperthermic treatment system.
U.S. Pat. Nos. 5,368,031 and 5,291,890 assigned to General Electric relate to an MRI controlled heating system in which a point source of heat generates a predetermined heat distribution which is then monitored to ensure that the actual heat distribution follows the predicted heat distribution to obtain an overall heating of the area to be heated. Again this patented arrangement has not led to a commercially viable hyperthermia surgical system.
U.S. Pat. No. 4,671,254 (Fair) assigned to Memorial Hospital for Cancer and Allied Diseases and issued Jun. 9, 1987, discloses a method for the non surgical treatment of tumors in which the tumor is subjected to shock waves. This type of treatment does not incorporate a monitoring system to monitor and control the effect of the shock waves.
U.S. Pat. No. 5,823,941 (Shaunnessey), not assigned, and issued Oct. 20, 1998, discloses a specially modified endoscope designed to support an optical fiber. The optical fiber emits light energy and may be moved longitudinally and rotated angularly about its axis to direct the energy. The device is used for excising tumors, and the energy is arranged to be sufficient to effect vaporization of the tissue to be excised. The gas formed during the process is removed by suction through the endoscope. An image of the tumor is obtained by MRI, which is thereafter used to program a path of movement of the fiber to be taken during the operation. Again, there is no feedback during the procedure to control the movement of the optical fiber, and the operation is wholly dependent upon the initial analysis. This arrangement has not achieved commercial or medical success.
U.S. Pat. No. 5,454,807 (Lennox) assigned to Boston Scientific Corporation and issued Oct. 3, 1995, discloses a device for use in irradiating a tumor with light energy from an optical fiber. A cooling fluid is supplied through a conduit within the fiber to apply surface cooling and to prevent surface damage while allowing increased levels of energy to be applied to deeper tissues. Once again, this arrangement does not provide feedback control of the heating effect.
U.S. Pat. No. 5,785,704 (Bille) assigned to MRC Systems GmbH and issued Jul. 28, 1996, also discloses a particular arrangement of a laser beam and lens for use in irradiation of brain tumors. In particular, this arrangement uses high speed pulsed laser energy for a photo-disruption effect, but does not disclose methods of feedback control of the energy.
Kahn, et al. in Journal of Computer Assisted Tomography 18(4):519-532, July/August 1994; Kahn, et al. in Journal of Magnetic Resonance Imaging 8: 160-164, 1998; and Vogl, et al. in Radiology 209: 381-385, 1998, all disclose a method of application of heat energy from a laser through a fiber to a tumor where the temperature at the periphery of the tumor is monitored during the application of the energy by MRI. McNichols, R J et al. in Lasers in Surgery and Medicine, 34:48-55, 2005, disclose energy control by an MRI feedback monitoring arrangement in a paper entitled “MR Thermometry-Based Feedback Control of LITT at 980 nm.” Additionally, the paper of Vogl discloses a cooling system supplied commercially by Somatex of Berlin, Germany for cooling the tissues at the probe end. The system is formed by an inner tube containing the fiber mounted within an outer tube. Cooling fluid is passed between the two tubes and inside the inner tube in a continuous stream.
While highly effective in certain applications, the use of ITT to treat brain tumors has been limited by the inability to focus the energy exclusively and precisely on the tumor so as to avoid damage to surrounding normal brain tissue. This is complicated by the fact that many brain tumors are highly irregular in shape.
Focused laser interstitial thermal therapy (f-LITT) is the next general refinement of laser-based thermal therapy technologies. In particular, f-LITT enables precise control over the deposition of heat energy, thereby enabling the physician to contain cell damage exclusively to within a tumor mass of virtually any size and shape. However, as with other ITT treatment systems, there is a need for an apparatus that allows a surgeon to precisely control the position of the treatment device within the tumor mass.
Therefore, a heretofore unaddressed need exists to establish a drive system for an elongate member that is capable of precisely controlling both the longitudinal and rotational positions of the elongate member with respect to a target, such as a tumor mass. Furthermore, what is needed is a drive system for an elongate member that is simple to use and that yields accurate and predictable results. The drive system should preferably be structured for use with any elongate medical device including, but not limited to, laser probes, catheters, endoscopes, and the like. The drive system should also preferably be manufactured from materials that make the system MRI-compatible.